1. Field of Invention
This application relates to the sequential placement of droplets of two or more liquids to a target location on a surface for the purpose of: removing material from the surface, as for the cleaning of delicate surfaces such as fossils, art objects, or semiconductor devices; adding material, such as precipitates, polymers, and agglomerates, to the surface; or using the surface to catalyze a reaction involving substances contained in the liquids, while minimizing the formation of side products.
2. Prior Art
Numerous methods exist for the application of a single liquid to a surface: manual or automated application with cloth, tissue, sponges, rollers, brushes or other applicators; droppers; streaming and aerosol sprayers; pressurized nozzles; and droplet jets. These methods do not readily facilitate rapid repeated alternate or sequential application of more than one liquid to the same place, location, or target. Devices which apply a single liquid to a surface depend upon a property of the liquid itself, such as drying and curing or dissolving and rinsing, to produce a desired effect of coating or cleaning on the surface. Inkjet technology can apply more than one color ink to a target location, but does not do so repeatedly to any great extent, and is designed for use with specially formulated inks rather than a variety of liquid solvents and reactive liquid chemical solutions. The ink droplets, even if applied to the same target location, do not produce their desired result by means of chemical reaction with one another while mixing on the surface to which they have been applied.
Different substances on the same surface may require different liquid solvents for dissolving and removing them. The power of solvation of some liquid solvents is reduced by mixing with another liquid solvent, so that a mixture of two or more liquid solvents is less effective than a separate application of each liquid solvent. Similar to liquid solvents, or more so in this respect, would be liquids containing acids and bases, which would neutralize each other if mixed before application to the surface. Material on a surface may in some cases contain components which yield to two different liquid solvents or other active liquid chemicals, which two liquid solvents or chemicals interfere with each other if applied simultaneously. In other cases a strongly solvent or reactive liquid may be required to cause any significant removal reaction, but must not be left in contact with the surface for too long, but must be applied and rinsed away or neutralized in a rapid and metered manner.
Semiconductor cleaning baths typically use one or more liquids in sequence, each liquid removing specific surface components. Components not yet removed by a subsequent suitable cleaning agent liquid may interfere with a current cleaning agent liquid.
Polymerizing and agglomerating mixtures that cure too rapidly are difficult or impossible to use, or at least require disposable one use mixing nozzles. Some glues cure so rapidly upon mixing of the two components that the compounds are mixed by simultaneous injection into a special tube or nozzle from which the mixed product is dispensed; such dispensers do not allow much hesitation, as for examination of how the material is being applied, before the mixing nozzle becomes clogged, and otherwise require attention to dexterous operation. This method excludes epoxies which cure yet more rapidly.
Liquid solutions which when combined produce a precipitate will in general do so with such rapidity that only traces if any of the precipitate would deposit onto a surface to which the previously mixed liquid solutions were subsequently applied. Otherwise, the alternate application of the liquid solutions by current means is tedious and results in scant precipitated deposits on the surface.
Plasma techniques can be used for cleaning and depositing, but the ionized gasses may be unsuitable for some surfaces, and chemically alter some deposit materials.
Both for methods of removal, as by solvents, and basic, acidic, oxidizing, reducing, enzymatic or other chemically active liquid solutions, and for methods of deposit, as of epoxies, polymers in general, organic adhesive aggregates, or precipitates, the alternate or sequential application of liquids without mechanical automation is tedious and of uncertain uniformity. Moreover, the action to be accomplished on the surface, whether of removal or of deposit, may require so many alternate applications as to not be expeditiously accomplished even by automated mechanical movement of the target surface or of the solution application baths or nozzles.
Some chemical reactions are catalyzed heterolytically by bringing the reactants into contact with a surface made up of a catalyzing material. In some cases it is desirable to bring the reactants into contact with a catalyzing surface as rapidly as possible so as to preclude the formation of undesirable side products caused by ordinary mixing of the liquid solutions containing the two reactants. A streaming application of two reactant solutions to a catalytic surface may involve some pre-mixing of the liquid solutions prior to intimate contact with the catalytic surface, with formation of undesirable side products.
This device and method allows rapid efficient alternate or sequential application of liquid cleaning agents to a surface, so as to maximize the total cleaning or removal effect despite surface deposits resistant to and thus interfering with any particular liquid cleaning agent. This device and method can be easily combined with current spinning substrate methods of semiconductor cleaning. This device and method allows for the precise adjustment of cleaning liquids to be applied to delicate surfaces such as artwork and fossils. The force with which droplets of removal liquids are applied to a surface can be varied for the application. In some embodiments, the alternate or sequential application of droplets is combined with a pulsed or continuous flow of a gas or gasses, which may include ionized gas or plasma. The force with which a gas or gas stream is applied can be varied for the application. This device or method allows flexibility, efficiency, and fine control in the cleaning or other surface removal of moderately small surfaces having a wide variety of physical and chemical characteristics.
Because the liquid components are not mixed prior to contact with the surface, this device or method facilitates the application of rapid curing polymeric or other aggregative substances without clogging of an applicator nozzle. Without using high temperature or ionized gasses, chemically sensitive precipitates can be deposited as an accumulated layer on surfaces which may themselves be sensitive to high temperatures or ionized charges. Radiations which facilitate the formation of a desired deposit product can be applied during the depositing process, rather than afterwards, allowing better penetration of the applied substances. The common target of the liquid orifices allows rapid application of more than one liquid without movement of the nozzle head or the object containing the target surface.
This device or method allows an individual liquid droplet applied to a catalytic surface to be flattened into a thin film on that catalytic surface before the application of a droplet of a reacting liquid, thereby minimizing the production of side products. Moreover, the catalytic surface can be periodically cleaned or restored while remaining in place.